1. Field of the Invention
The present invention relates to a semiconductor device provided with a stiffener.
2. Description of the Related Art
In a semiconductor device having a semiconductor element mounted on a substrate, a problem arises in that a warp may occur in the substrate and in the semiconductor element as a result of a difference between the coefficient of thermal expansion of the semiconductor element and that of the substrate. Accordingly, there have been proposals wherein a stiffener (a reinforcement member) is attached to the surface of the substrate opposite to that mounting the semiconductor element thereon to prevent the substrate and the semiconductor element from warping (for example, see Japanese Unexamined Patent Publication No. 3-295263, No. 6-204656, Japanese Unexamined Patent Publication No. 6-4579, No. 8-153938, No. 6-82839, No. 11-260953, No. 2000-174176, No. 2001-101375, No. 2001-15561, No. 2002-231769, and No. 2002-252301).
Because the rigidity of the substrate increases if a metallic stiffener is attached to the substrate, the substrate is resistant against the bending to minimize the warp of the substrate and of the semiconductor element. In this case, if the coefficient of thermal expansion of the stiffener is made to be the same level as that of the substrate, the warp of the substrate and the semiconductor element can be even further reduced. However, because the warp of the substrate and that of the semiconductor element are not completely eliminated, there is still a requirement for further reducing the warp of the substrate and of the semiconductor element.